1. Field of the Invention
The present invention relates to a card connector, especially a card connector having a contact terminal which has a split spring bar that is twisted, and the contact terminal for the card connector.
2. Background Technology
Many of recent electronics such as a cellular phone, PDA, personal computer, and digital camera include an IC card which is loaded with IC or memory, and reads and writes data in the loaded IC card. Usually, in such an electronic device, a card connector is provided inside of the device, or can be attached to the exterior of the device. A plurality of contact terminals for the card connector (hereinafter, “contact terminals”) are arranged in the card connector, and by contacting the contact terminals with the card, data can be read or written. For example, the contact terminals include a signal terminal for signal transmission, a power terminal to supply electric power, and a ground terminal to connect a card to ground.
Usually each contact terminal has only one counter contact section for contacting with one contact section (e.g. contact pad) of the card. However, in order to improve reliability of the contact, there is a contact terminal, which has a plurality of counter contact sections for contacting with one contact section of the card. Among contact terminals, especially the power terminal and the ground terminal could significantly affect card data by the contact condition between those terminals and the contact section of the card. Therefore, there is a demand to improve the contact condition.
As an example of a conventional contact terminal, in which a plurality of counter contact sections are provided on one contact terminal, Unexamined Japan Patent Application Publication 2002-100440 is disclosed. This patent publication discloses a contact terminal, which has two counter contact sections. A perspective view of the contact terminal disclosed in the patent publication is shown in FIG. 11(a). An enlarged cross-sectional view of FIG. 11(a) taken along line A—A is shown in FIG. 11(b). Here, in FIG. 11(b), the card that contacts with the contact terminal is also partially shown. In this contact terminal 1, the end portion, i.e. spring bar 11 which can be elastically displaced and will contact with the card, is split into two portions along the longitudinal direction, and has two split spring bars 110 and 110′.
Those two split spring bars 110 and 110′ can individually contact with the contact section 14 of the card at counter contact sections provided near the ends. The split spring bars 110 and 110′ have different spring constants from each other, so as to prevent instantaneous break between the split spring bars 110, 110′ and the contact section 14 of the card. Therefore, the resonance frequencies (natural frequencies) are differed between those split spring bars 110 and 110′. Even if the counter contact sections 114 and 114′ of the split spring bars 110 and 110′ come off from the contact section 14 of the card by impact or vibration, they contact with the contact section 14 at different resonance frequencies, so that the connection between the split spring bars 110, 110′ and the contact section of the card can be maintained all the time.
Accordingly, the instantaneous break can be prevented. Here, as a method of changing the spring constants, a split spring bar can be partially differed from the other, especially in length, width, thickness or material of the portion that functions as a spring. For example, the above-listed patent publication discloses split spring bars 110 and 110′ having different widths, and split spring bars 110 and 110′ having different length due to different bending angles of the portions that function as a spring.
In case of such contact terminal having a plurality of contact sections, the plurality of contact sections have to contact with one narrow contact section of the card. Therefore, the dimension “c” between the counter contact sections 114 and 114′ along the width direction has to be narrow as shown in FIG. 11(a). Especially, in case of having a plurality of contacts, a plurality of split spring bars 110 and 110′ have to be formed according to the above-described limitation on the dimension. In addition, if the spring constants are differed between those split spring bars by differing the width of one split spring bar from that of the other, as in the example of conventional one shown in FIGS. 11(a) and 11(b), for example, the width “e” of the split spring bar 110′ has to be extremely narrow.
If the split spring bar has such extremely narrow width “e”, it cannot satisfactorily perform as a spring, and therefore it becomes very difficult to ensure satisfactory contact pressure between the split spring bar and the contact section 14 of the card (See f and g in FIG. 11(b)). As one method to solve this problem, the gap “a” between the split spring bars 110 and 110′ can be reduced. However, since the gap “a” has to be larger than a certain dimension in view of preventing damaging a press tool at the time of inserting it into the gap, such method cannot be employed. Accordingly, in order to obtain ideal split spring bars, the width (especially “e”) of each split spring bar has to be larger than a certain dimension in order to ensure enough contact pressure to the contact section of the card.
In addition, the gap “a” has to be larger than a certain dimension in order to prevent damaging a press tool, and the dimension between the contact points (portions) of the counter contact sections of the split spring bars has to be limited to a specified width “c”.